In the prior art, used in semiconductor production plants for example, chambers installed in clean rooms are vacuum exhausted, process gases are introduced into evacuated chambers and the procedure of the reaction with the process gas is performed inside the relevant chamber.
The gas produced by the reaction with the process gas (the reaction product gas) in the said chamber and the residuum of the process gas in the said chamber are exhausted to the exterior of the said chamber by a vacuum exhaust system.
FIG. 2 is a block diagram of vacuum exhaust system of the prior art. The vacuum exhaust system S2 shown in FIG. 2 has a structure comprising a plurality of chambers 1 (1A, 1B, . . . 1n). The vacuum exhaust system which exhausts the gases from the plurality of chambers is described in, for example, JP 1-159475 (A) and JP 3564069 (A).
Since, in the vacuum exhaust system S2 shown in FIG. 2, the components of the exhaust system which exhausts gas from the first chamber 1 (1A) are identical with the components of the exhaust systems which exhaust gas from the other chambers 1 (1B, . . . 1n), only the exhaust system which exhausts gas from the first chamber 1 (1A) is described below.
The vacuum exhaust system S2, shown in FIG. 2 has a first channel 50A and second channel 50B as the channels through which gas is exhausted from the chamber 1 (1A).
A turbomolecular pump 51 which functions as a gas exhaust means for the gas molecular flow region is fitted into the upstream end of the first channel 50A. This first channel 50A is split into a first branch channel 50A-1 and second branch channel 50A-2 at a position downstream from the turbomolecular pump 51.
A combination dry pump 52 is fitted to the downstream end of the first branch channel 50A-1 to exhaust the gas produced by the reaction with the process gas (the reaction product gas) in the first chamber 1 and the residuum of the process gas in the first chamber 1.
On the other hand, a combination dry pump 53 is fitted to the downstream end of the second branch channel 50B-2 to exhaust the gas used for the cleaning of the interior of the chamber 1.
Furthermore, a dry pump 54 is fitted to the downstream end of the first channel 50A as the rough pump used when gas is initially exhausted from the chamber 1.
The said combination dry pumps 52, 53 comprise a pump body P1 such as a known screw pump, which functions as a gas exhaust means in the viscous flow region of the gas, and a so-called mechanical booster pump P2 which functions as a means of increasing the exhaustion rate in the pressure region in which the exhaustion rate of the pump body P1 is lower.
However, in the vacuum exhaust system S2, as shown in FIG. 2, during rough pumping of the chamber 1 (1A) all the valves V1, V2 and V3 fitted to the first channel 50A and branch channels (first branch channel 50A-1 and second branch channel 50B-2) are closed and the valve V4 fitted to the second channel 50B is open, so that exhaustion of gas through first channel 50A is disabled and exhaustion of gas through second channel 50B is enabled. Also, rough pumping of chamber 1 is performed through the second channel 50B, by the exhausting action of the dry pump 54.
Furthermore, in the vacuum exhaust system S2, as shown in FIG. 2, when the gas produced by the reaction with the process gas (the reaction product gas) in the chamber 1 (1A) and the residuum of the process gas in the chamber 1 are exhausted, valve 4 in the second channel 50B and valve V3 of the second branch channel 50A-2 are closed, and the valve V1 of the first channel 50A and valve V2 of the first branch channel 50A-1 are open, so that exhaustion of gas through second channel 50B and through second branch channel 50A-2 is disabled and exhaustion of gas through the first branch channel 50A-1 is enabled. Thus the gas (reaction product gas and residuum process gas) in chamber 1 is exhausted through the first channel 50A (using the first branch channel 50A-1) by the exhausting action of turbomolecular pump 51 and dry pump 52.
Furthermore, in the vacuum exhaust system S2, as shown in FIG. 2, when the gas (cleaning gas) used to clean the interior of the chamber 1 (1A) is exhausted, valve 4 in the second channel 50B and valve 2 of the first branch channel 50A-1 are closed, and the valve 1 of the first channel 50A and valve 3 of the second branch channel 50A-2 are open, so that exhaustion of gas through second channel 50B and through first branch channel 50A-1 is disabled and exhaustion of gas through the second branch channel 50A-2 is enabled. Thus, cleaning gas in chamber 1 and the turbomolecular pump 52 is exhausted through the first channel 50A (using the second branch channel 50A-2) by the exhausting action of the dry pump 53.
Since, however, with the structure of the vacuum exhaust system S2, described above, as shown in FIG. 2, since valve V2 and V3 are located immediately before, respectively, dry pump 52 and dry pump 53, the first channel 50A and second channel 52B coexist from the beginning to the end of the exhaust system as the exhaust system from the chambers 1 to dry pumps 52, 53 and 54 etc, there are the problems that the overall structure of the vacuum exhaust system S is complex and the cost is higher as a consequence.